Balloon catheter having a shaft with a variable stiffness inner tubular member

ABSTRACT

A catheter having an elongated shaft and a balloon on a distal shaft section, the elongated shaft comprising an outer tubular member, and an inner tubular member which has a bonded portion along which an outer surface of the inner tubular member is bonded to an inner surface of the outer tubular member. The inner tubular member has a proximal portion proximal to the bonded portion, and a distal portion distal to the bonded portion with higher axial compression stiffness and column strength than the proximal portion thereof. The catheter has improved trackability, axial collapse resistance, pushability, and crossability, for improved ability to position the balloon at a desired location in a patient&#39;s body lumen.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a division of U.S. Ser. No. 13/224,917 filed Sep. 2,2011, which is a division of U.S. Ser. No. 11/844,117, filed Aug. 23,2007; now U.S. Pat. No. 8,012,300, which is a division of U.S. Ser. No.10/392,697 filed Mar. 20, 2003, now U.S. Pat. No. 7,273,485.

BACKGROUND

This invention generally relates to catheters, and particularlyintravascular catheters for use in percutaneous transluminal coronaryangioplasty (PTCA) or for the delivery of stents.

In percutaneous transluminal coronary angioplasty (PTCA) procedures aguiding catheter is advanced in the patient's vasculature until thedistal tip of the guiding catheter is seated in the ostium of a desiredcoronary artery. A guidewire is first advanced out of the distal end ofthe guiding catheter into the patient's coronary artery until the distalend of the guidewire crosses a lesion to be dilated. A dilatationcatheter, having an inflatable balloon on the distal portion thereof, isadvanced into the patient's coronary anatomy over the previouslyintroduced guidewire until the balloon of the dilatation catheter isproperly positioned across the lesion. Once properly positioned, thedilatation balloon is inflated with inflation fluid one or more times toa predetermined size at relatively high pressures so that the stenosisis compressed against the arterial wall and the wall expanded to open upthe vascular passageway. Generally, the inflated diameter of the balloonis approximately the same diameter as the native diameter of the bodylumen being dilated so as to complete the dilatation but not over expandthe artery wall. After the balloon is finally deflated, blood resumesthrough the dilated artery and the dilatation catheter and the guidewirecan be removed therefrom.

In such angioplasty procedures, there may be restenosis of the artery,i.e., reformation of the arterial blockage, which necessitates eitheranother angioplasty procedure, or some other method of repairing orstrengthening the dilated area. To reduce the restenosis rate ofangioplasty alone and to strengthen the dilated area, physicians nownormally implant an intravascular prosthesis, generally called a stent,inside the artery at the site of the lesion. Stents may also be used torepair vessels having an intimal flap or dissection or to generallystrengthen a weakened section of a vessel or to maintain its patency.Stents are usually delivered to a desired location within a coronaryartery in a contracted condition on a balloon of a catheter which issimilar in many respects to a balloon angioplasty catheter, and expandedwithin the patient's artery to a larger diameter by expansion of theballoon. The balloon is deflated to remove the catheter and the stentleft in place within the artery at the site of the dilated lesion. Fordetails of stents, see for example, U.S. Pat. No. 5,507,768 (Lau, etal.) and U.S. Pat. No. 5,458,615 (Klemm, et al.), which are incorporatedherein by reference.

An essential step in effectively performing a PTCA procedure is properlypositioning the balloon catheter at a desired location within thecoronary artery. To properly position the balloon at the stenosedregion, the catheter must have good pushability (i.e., ability totransmit force along the length of the catheter), and good trackabilityand flexibility, to be readily advanceable within the tortuous anatomyof the patient's vasculature. Conventional balloon catheters forintravascular procedures, such as angioplasty and stent delivery,frequently have a relatively stiff proximal shaft section to facilitateadvancement of the catheter within the patient's body lumen and arelatively flexible distal shaft section to facilitate passage throughtortuous anatomy such as distal coronary and neurological arterieswithout damage to the vessel wall. However, one difficulty has beenproviding a catheter shaft having low bending stiffness for optimumtrackability, while having sufficiently high axial stiffness(compression modulus) and column strength (collapse point) for maximumtransmission of force to the catheter distal end. A shaft inner tubularmember (extending through the balloon interior) having inadequate columnstiffness may telescopically collapse under axial load causing balloonbunching/buckling during advancement of the catheter, which consequentlyinhibits positioning the balloon across a stenosis. Accordingly, itwould be a significant advance to provide a catheter having an improvedcombination of flexibility, collapse resistance, pushability, andcrossability.

SUMMARY OF THE INVENTION

The invention is directed to a balloon catheter having an elongatedshaft and a balloon on a distal shaft section, the elongated shaftcomprising an outer tubular member, and an inner tubular member with abonded portion along which an outer surface of the inner tubular memberis bonded to an inner surface of the outer tubular member. The innertubular member has a distal portion distal to the bonded portion withhigher axial compression stiffness and column strength than a proximalportion of the inner tubular member. The catheter has improvedtrackability, axial collapse resistance, pushability, and crossability,for improved ability to position the balloon at a desired location in apatient's body lumen.

A balloon catheter of the invention generally comprises an elongatedshaft having a proximal shaft section, a distal shaft section, aninflation lumen, and a guidewire lumen, with a balloon on a distal shaftsection. The elongated shaft is formed at least in part by an outertubular member defining at least a section of the inflation lumen influid communication with an interior of the balloon, and by an innertubular member defining at least a section of the guidewire lumen. Theinner tubular member extends in at least a distal section of the outertubular member and in the interior of the balloon, and in accordancewith the invention has a bonded portion bonded to the outer tubularmember. The guidewire lumen is in fluid communication with a proximalguidewire port, and a distal guidewire port at the distal end of theshaft. In one embodiment, the catheter is a rapid exchange type catheterhaving the proximal end of the inner tubular member in the distal shaftsection located distal to the proximal end of the shaft, so that theguidewire proximal port is in the distal shaft section spaced arelatively short distance proximally from the guidewire distal port anda relatively long distance distally from the proximal end of thecatheter shaft. In an alternative embodiment, the catheter is anover-the-wire type catheter having the inner tubular member proximal endlocated at a proximal end portion of the shaft so that the inner tubularmember extends along the proximal and distal shaft sections.

The bonded portion of the inner tubular member links the inner tubularmember to the outer tubular member, preferably at or adjacent to astiffness transition in the inner tubular member. Specifically, a distalportion of the inner tubular member located distal to the bonded portionhas a higher axial compression stiffness and column strength than aproximal portion of the inner tubular member located proximal to thebonded portion. Additionally, in one embodiment, the proximal portion ofthe inner tubular member has a lower bending stiffness than the distalportion of the inner tubular member. Preferably, the bonded portion islocated at (i.e., radially aligned with) or longitudinally adjacent tothe proximal end of the balloon. In a presently preferred embodiment,the bonded portion has a distal end located proximal to the balloon andtypically a relatively short distance from the proximal end of theballoon and a relatively long distance from the proximal end of theinner tubular member. As a result, the length of the distal portion ofthe inner tubular member extending distally from the bonded portion,through the balloon interior to the distal end of the inner tubularmember, is minimized relative to the length of the proximal portion ofthe inner tubular member. The configuration provides a maximum length tothe highly flexible proximal portion of the inner tubular member. In oneembodiment, the distal portion of the inner tubular member has a lengthequal to about 1 to about 5% of the length of the entire shaft. Bylinking a portion of the inner tubular member to the outer tubularmember near the proximal end of the balloon, the axial compressionstiffness of the proximal portion of the inner tubular member has littleor no influence on the amount of axial load that is carried by theballoon. Consequently, in the catheter of the invention, the innertubular member proximal portion has a low bending stiffness and aconcurrently low axial stiffness, with the outer tubular member carryinga substantial portion of the total axial force along the shaft up to theadjoining balloon. Distal to the outer tubular member, the distalportion of the inner tubular member is provided with sufficient columnstiffness and strength to prevent or inhibit it from elasticallyshortening or telescopically collapsing under axial load. As a result,the catheter shaft is highly flexible, and nonetheless transfers themajority of applied axial load to the distal end of the balloon andthereby prevents or inhibits buckling of the balloon during advancementof the catheter in the patient's body lumen.

The inner tubular member proximal portion typically is constructed so asto minimize its bending stiffness, thereby being less stiff in bothbending stiffness and axial compression stiffness than the outer tubularmember. The outer tubular member is provided with sufficient axialcompression stiffness to carry a majority of the axial load withoutbuckling. For example, in one embodiment, the proximal inner membercarries only about 5 to about 25% of the total axial force transmittedto the distal end of the catheter. In one embodiment, the catheter ispreferably an over-the-wire type catheter, due to the large reduction inthe axial load carried by the balloon provided by the catheterconfiguration of the invention. In one embodiment, the axial loadcarried by the balloon in an over-the-wire catheter of the invention islowered by about 40 to about 90%, compared to a conventional catheterwithout the inner tubular member bonded portion. In one embodiment, theaxial load carried by the balloon in a rapid exchange catheter of theinvention is lowered by about 40 to about 80%, compared to aconventional catheter without the inner tubular member bonded portion.

A variety of suitable methods may be used to form the inner tubularmember stiffness transition between the proximal and distal portionsthereof, to provide an inner member with a relatively low bendingstiffness over the majority of its length but having greater axialstiffness (also known as compression modulus) and column strength (i.e.,collapse point under axial load) distal to the bonded portion. In apresently preferred embodiment, at least part of the inner tubularmember proximal portion has a first wall thickness, and at least part ofthe inner tubular member distal portion has a second wall thicknessgreater than the first wall thickness. Preferably, the part of the innertubular member having the first wall thickness has an outer diametersmaller than an outer diameter of the part of the inner tubular memberhaving the second (i.e., smaller) wall thickness, which thus increasesthe size of the inflation lumen defined by the space between theproximal portion of the inner tubular member and the inner surface ofthe outer tubular member. The variable wall thickness can be formedusing a variety of processing methods during manufacture of the innertubular member, including decreasing (as for example by necking) thewall thickness of the proximal portion and/or increasing the wallthickness of the distal portion. In an alternative embodiment, thedistal portion of the inner tubular member is provided with the higheraxial stiffness. For example, the axial stiffness of the distal portioncan be increased by providing a reinforcing member (such as braiding, ora mandrel, or a flexible tubular splint member on an outer surfacethereof), or by adding fiber reinforcement to the shaft jacketing, or byirradiating or heat stabilizing the polymeric material of the distalportion to increase its stiffness. In another embodiment, the innertubular member distal portion is formed of a polymeric material having ahigher Shore durometer hardness than the polymeric material of theproximal portion of the inner tubular member. The inner tubular membertypically comprises a multilayered tubular member, so that theembodiment with a higher durometer polymeric material in the distalportion should be understood to refer to the durometer of at least oneof the layers of the inner tubular member. The higher durometer materialforming the distal portion may be the same type of polymeric material asthe polymeric material of the proximal portion (i.e., a polyamide), oralternatively, a different type of polymeric material.

The bonded portion extends around part of the circumference of the innertubular member, so that a nonbonded portion of the inner tubular memberis radially adjacent to the bonded portion to provide a path for theinflation fluid past the bonded portion. The bonded portion generallyextends around about 10% to about 90% of the circumference of the innertubular member, and most preferably the percentage is minimized in orderto maximize the fluid flow path past the bond. The length of the bondedportion is generally substantially less than the length of the innertubular member, although in one embodiment, the inner tubular memberincludes one or more portions proximally spaced apart from the bondedportion, along which the outer surface of the inner tubular memberproximal portion is bonded to the inner surface of the outer tubularmember.

In a presently preferred embodiment, the inner tubular member comprisesa polymeric tube with a coiled reinforcing member embedded therein.Although the distal portion of the inner tubular member typically has ahigher axial compression stiffness and column strength than the proximalportion thereof, the coiled reinforcing member allows the inner tubularmember to have a relatively low bending stiffness and high radialcollapse resistance throughout, for excellent catheter trackability andguidewire movement even after inflation of the balloon at relativelyhigh inflation pressures. The coiled reinforcing member preferablyextends at least in part within the proximal and distal portions of theinner tubular member, and in one embodiment, the coiled reinforcingmember extends along the entire length of the inner tubular member. Inone embodiment, the coiled reinforcing member has a uniform pitch,stiffness, and/or column strength throughout its length. Alternatively,the coiled reinforcing member extending along the distal portion of theinner tubular member has a tighter coil pitch (i.e., more closely spacedcoils) than along the proximal portion of the inner tubular member, orotherwise provided with a higher axial stiffness and column strengthalong the distal portion, to produce the stiffer distal portion of theinner tubular member. For example, a longitudinally extending wiremember bonded to the distal portion of the coiled reinforcing memberselectively stiffens the distal portion of the inner tubular member. Inone embodiment, two types or plies of wire or ribbon form thereinforcing member, with the first type reinforcing the entire length ofthe inner tubular member and the second type located in the distalportion of the inner tubular member to selectively stiffen the distalportion of the inner tubular member by, for example, preventing thedistal coils from moving closer together or bunching under axial load.Similarly, a braided reinforcing member having a variable pick count(number of braid crossover points per unit of axial length) imparting astiffness transition may alternatively be used to form the inner tubularmember. The resulting catheter shaft, formed by the inner and outertubular members, has an improved low bending stiffness throughout thelength of the inner member, for improved trackability.

In a method of making a balloon catheter embodying features of theinvention, an elongated shaft having a proximal end, a distal end, aninflation lumen, and a guidewire lumen is assembled by placing an innertubular member within at least a distal section of an outer tubularmember, so that the inner tubular member defines the guidewire lumen andthe outer tubular member defines the inflation lumen, the inner tubularmember having a proximal portion with an axial compression stiffness andbending stiffness less than an axial compression stiffness and bendingstiffness of a distal portion of the inner tubular member. A portion ofthe inner tubular member is then bonded to the outer tubular member ator adjacent a junction between the proximal and distal portions of theinner tubular member, to form a bonded portion along which an outersurface of the inner tubular member is bonded to an inner surface of theouter tubular member. A balloon is bonded to the distal shaft section sothat the balloon has an interior in fluid communication with theinflation lumen, to form the balloon catheter.

The inner tubular member having a stiffness transition can be formedusing a variety of suitable methods. For example, in one embodiment,forming the inner tubular member comprises necking a proximal part of apolymeric tube to reduce a wall thickness and an outer diameter thereofwithout reducing an inner diameter thereof, to thereby reduce the axialcompression stiffness of the proximal part of the polymeric tube, andembedding a coiled reinforcing member in the polymeric tube. In anotherembodiment, forming the inner tubular member comprises increasing thewall thickness of a distal section of a polymeric tubular member havinga coiled reinforcing member embedded therein, by a method selected fromthe group consisting of heat shrinking an outer polymeric layer onto thedistal section of the coil reinforced polymeric tubular member, meltbonding an outer polymeric layer onto the distal section of the coilreinforced polymeric tubular member, or dip coating the distal sectionof the coiled reinforced polymeric tubular member. In anotherembodiment, forming the inner tubular member comprises joining thedistal end of a first tube to a proximal end of a second tube to form apolymeric tubular member, and fusing the polymeric tubular member to acoiled reinforcing member, and the second tube is formed of a polymericmaterial having a higher Shore durometer hardness or has a wallthickness greater than a wall thickness of the first tube. In anotherembodiment, forming the inner tubular member comprises fusing apolymeric tube to a braided reinforcing member, the braided reinforcingmember having a distal part with a pick count which is higher than apick count of a proximal part of the braided reinforcing member. Inanother embodiment, forming the inner tubular member comprises applyingan adhesive or melt bondable polymer to a portion of a mandrel, andapplying a coil on the mandrel with a distal part of the coil on theadhesive or melt bondable polymer, and fusing a polymeric layer on thecoil, to form the coil reinforced polymeric tubular member. In anotherembodiment, forming the inner tubular member comprises joining thedistal end of a coil reinforced polymeric tubular member to the proximalend of a polymer tube having a greater axial stiffness and columnstrength than the coil reinforced polymeric tubular member. In anotherembodiment, forming the inner tubular member comprises irradiating orheat stabilizing a distal part of a polymeric tube to increase thestiffness of the distal part of the polymeric tube.

The balloon catheter of the invention has improved pushability andtrackability, due to the low bending stiffness inner tubular memberhaving a bonded portion bonded to the outer tubular member and excellentforce transmission through the balloon interior to the distal tip. Theshaft configuration prevents or inhibits the balloon from buckling orbunching during advancement in the patient's blood vessel, despite thelow bending stiffness of the inner tubular member and resultingexcellent trackability. Thus, the catheter shaft of the inventionaccommodates typically competing considerations in the design ofcatheters, to facilitate positioning the balloon at a desired locationin the patient's blood vessel. These and other advantages of theinvention will become more apparent from the following detaileddescription of the invention and the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, partially in section, of a rapid exchangetype balloon catheter which embodies features of the invention.

FIG. 2-3 are transverse cross sections of the catheter shown in FIG. 1,taken along lines 2-2 and 3-3, respectively.

FIG. 4 is an enlarged, longitudinal cross sectional view of the cathetershown in FIG. 1, taken within circle 4.

FIG. 5 is a transverse cross section of the catheter shown in FIG. 4,taken along line 5-5.

FIG. 6 is an elevational view, partially in section, of an over-the-wiretype balloon catheter which embodies features of the invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates rapid exchange type balloon catheter 10 embodyingfeatures of the invention. Catheter 10 generally comprises an elongatedcatheter shaft 11 having a proximal end, a distal end, a proximal shaftsection 12 and a distal shaft section 13 at the distal end of theproximal shaft section, and an inflatable balloon 14 on the distal shaftsection. The shaft 11 has an inflation lumen 21, and a guidewirereceiving lumen 22. The proximal shaft section 12 comprises a proximaltubular member defining a proximal portion of the inflation lumen 21.The distal shaft section 13 comprises an outer tubular member 19defining a distal portion of the inflation lumen 21, and an innertubular member 20 defining the guidewire lumen 22 in fluid communicationwith a guidewire distal port 24 at the distal end of the catheter and aguidewire proximal port 25 at the proximal end of the inner tubularmember 20, configured to slidably receive guidewire 23 therein. Balloon14 has a proximal end sealingly secured to the distal end of outertubular member 19 and a distal end sealingly secured to the distal endof inner tubular member 20, so that its interior 15 is in fluidcommunication with inflation lumen 21. An adapter 17 at the proximal endof the catheter provides access to the inflation lumen 21. FIG. 1illustrates the balloon 14 in a low profile configuration, prior toinflation, for introduction and advancement within the patient's bodylumen 18, with a stent 16 mounted on the working length of the balloon14. In use, the distal end of catheter 10 is advanced to a desiredregion of the patient's body lumen 18 in a conventional manner eitherover previously positioned guidewire 23, or with guidewire 23 already inthe catheter 10. The balloon 14 is inflated to expand the stent 16, andthe balloon deflated, and the catheter 10 removed from or repositionedwithin the body lumen 18, leaving stent 16 implanted in the body lumen18. Although illustrated as a stent delivery catheter in the embodimentof FIG. 1, the balloon catheter 10 of the invention may be configured toperform a variety of medical procedures including dilating a stenosis.Similarly, rapid exchange type catheter 10 of the embodiment of FIG. 1may comprise a variety of suitable rapid exchange catheter shaftconfigurations as are conventionally known. FIGS. 2 and 3 illustratetransverse cross sectional views of the catheter of FIG. 1, taken alonglines 2-2 and 3-3, respectively.

The inner tubular member 20 has a bonded portion 30 along which theouter surface of the inner tubular member is bonded to the inner surfaceof the outer tubular member 19, as best shown in FIG. 4, illustrating anenlarged longitudinal cross section of the catheter of FIG. 1, takenwithin circle 4. The bonded portion is proximally adjacent to theproximal end of the balloon 14, with a distal end proximal to theballoon 14. The bonded portion 30 is typically spaced proximally apartfrom the proximal end of the balloon a sufficient distance, so thatforming the bonding portion 30 does not damage the balloon 14 secured tothe outer tubular member 19. For example, in one embodiment, the distalend of the bonded portion is within about 0.5 to 2 cm from the proximalend of the balloon. However, the bonded portion 30 can have a variety ofsuitable locations. For example, the bonded portion 30 can alternativelyextend at least in part underneath the balloon proximal skirt section(i.e., radially aligned therewith), with the distal end of the bondedportion located distal to the proximal end of the balloon, provided theballoon 14 is not damaged by the bonding process.

Preferably, the bonded portion 30 length is about 0.1 to about 2 cm,which in the rapid exchange catheter of FIG. 1 is about 0.4% to about 8%of the length of the inner tubular member 20 (the inner tubular member20 having a length of about 20 to about 30 cm). The bonded portion 30extends partially around the circumference of inner tubular member 20,as best shown in FIG. 5 illustrating a transverse cross section of FIG.4, taken along line 5-5. In the illustrated embodiment, the bondedportion extends around about 30% to about 40% of the inner tubularmember circumference.

In one embodiment, the bonded portion 30 is formed by heating andapplying a radially inward force to press a portion of the outer tubularmember 19 down onto the underlying inner tubular member 20 using acrescent shaped mandrel to preserve the inflation lumen. As a result,the outer diameter of the distal shaft 13 is decreased along the bondedportion 30. The inflation lumen 21 and guidewire lumen 22 are in aside-by-side relation along the length of the bonded portion 30. In theembodiment of FIG. 1, proximal to the bonded portion 30, the outer andinner tubular members 19, 20 are separate as best illustrated in FIG. 2,although they may be intermittently bonded in like manner at other moreproximal locations. A continuous bond line is not recommended howeverbecause of the accompanying increase in bending stiffness. The bondbetween the outer and inner tubular members 19, 20 along the bondedportion 30 is preferably a fusion bond, although the bond mayalternatively or additionally be an adhesive bond. For example, theouter and inner tubular members 19, 20 are heated along the length ofthe desired bonded portion, typically with a mandrels in the lumens 21,22 and heat shrink tubing (not shown) positioned around the outertubular member 19, to soften and melt bond the tubular members together.The tubular members 19, 20 are preferably heated using a laser and theheat directed only along the part of the circumference of the outertubular member to be bonded to the inner tubular member to reduce heatspread during formation of bonded portion 30. However, a variety ofsuitable heating methods may be used including using a hot air heatingnozzle and heating the entire circumference of the outer tubular member.

In the embodiment illustrated in FIG. 4, the bonded portion 30 is formedby directly bonding the outer and inner tubular members 19, 20 together.However, in an alternative embodiment, a tube (not shown) may beprovided in the inflation lumen 21 which has an outer surface bonded toboth the outer surface of the inner tubular member and to the innersurface of the outer tubular member, to thereby bond the outer and innertubular members together to form bonded portion 30 (i.e., the tube isonly on one side of the inner tubular member), and the inner tubularmember may therefore be coaxial with the outer tubular member.

The inner tubular member 20 has a proximal portion proximal to thebonded portion 30, and a distal portion distal to the bonded portion 30.The distal portion of the inner tubular member 20 has a higher axialcompressive stiffness and column strength than the proximal portion ofthe inner tubular member 20. In the embodiment of FIG. 4, the distalportion of the inner tubular member 20 has a larger wall thickness and alarger outer diameter than the proximal portion of the inner tubularmember 20, although a variety of suitable methods may be used to providethe inner tubular member stiffness transition. The reduced outerdiameter of the proximal portion of the inner tubular member 20increases the size of the inflation lumen 21 extending therealong, formore rapid inflation/deflation. Additionally, the smaller wall thicknessof the proximal portion of the inner tubular member 20 provides theproximal portion of the inner tubular member 20 with a lower bendingstiffness than the distal portion thereof.

In the embodiment of FIG. 4, the wall thickness of the inner tubularmember 20 along the bonded portion 30 is greater than the wall thicknessof the inner tubular member proximal portion. Specifically, the proximalend of the bonded portion 30 is radially aligned with the proximal endof the part of the inner tubular member having the larger wall thicknessthan the proximal portion of the inner tubular member. The stiffnesstransition provided by the change in wall thickness of the inner memberpreferably takes place over a relatively short length, to providemaximum benefit of the lower bending stiffness of the proximal innermember. In the embodiment of FIG. 4, the outer diameter of the innertubular member tapers proximally to the smaller outer diameter of theproximal portion along a length of about 1 mm.

The inner tubular member preferably comprises a polymeric tube 31 with acoiled reinforcing member 32 embedded therein. In the embodiment of FIG.4, the coiled reinforcing member 32 is a coiled flat ribbon, spiralingalong the length of the inner tubular member with uniformly spaced-apartcoils. However, a variety of suitable reinforcing members may be used asare conventionally known, including a coiled round wire. The coiledreinforcing member extends at least in part within the proximal anddistal portions of the inner tubular member 20, and preferably extendsalong substantially the entire length of the inner tubular member 20 toprevent radial collapse under extreme balloon inflation pressures.Although the polymeric tube 31 is shown as a single layered member forease of illustration, it should be understood that the polymeric tube 31is typically a multilayered polymeric member, as for example with aninner lubricious polymeric layer, and an outer polymeric layercoextruded or heat shrunk around the inner polymeric layer, with thecoiled member 32 embedded in one or both layers. Typically, the extrudedsingle or multilayered polymeric tube is necked to reduce the inner andouter diameter thereof. In a presently preferred embodiment, the reducedwall thickness proximal portion of the inner tubular member 20 is thenformed by necking the proximal part of the extruded tube to reduce awall thickness and an outer diameter thereof without reducing an innerdiameter thereof. Alternatively, an outer layer of polymeric materialmay be provided on the outer surface of the inner tubular member distalto the proximal portion of the inner tubular member, as for example byheat shrinking a polymeric tube down onto the distal portion of theinner tubular member, to increase the wall thickness and axialcompression stiffness of the inner tubular member distal portionrelative to the proximal portion thereof.

The axial compression stiffness and column stiffness of the distalportion of the inner tubular member 20 are about the same as those ofthe entire length of an inner tubular member in a conventional catheter.However, the bending stiffness of the proximal portion of the innertubular member 20 is as low as can be practically attained in order tominimize the catheter's overall bending stiffness there.

In one embodiment (not shown), the inner tubular member includes one ormore portions proximally spaced apart from the bonded portion, alongwhich the outer surface of the inner tubular member proximal portion isbonded to the inner surface of the outer tubular member. In oneembodiment, the inner tubular member has a plurality of these portionsbonded to the outer tubular member which are intermittently spaced apartfrom one another with portions of the inner tubular member therebetweenwhich are not bonded to the outer tubular member.

In the embodiment of FIG. 1, the catheter 10 is a rapid exchangecatheter. In an alternative embodiment, the catheter is an over-the-wirecatheter, so that the guidewire proximal port is at the proximal end ofthe catheter shaft. FIG. 6 illustrates an over-the-wire type ballooncatheter 40 embodying features of the invention, generally comprising ashaft 41 having a proximal shaft section 42 and a distal shaft section43, and a balloon 44 on the distal shaft section. The elongated shaftcomprises an outer tubular member 45 defining an inflation lumen 46, andan inner tubular member 47 defining a guidewire lumen 48 configured toslidably receive a guidewire 23 therein. Inner tubular member 47,extending within the proximal and distal shaft sections 42, 43, extendsdistally beyond the distal end of the outer tubular member 45 andthrough the interior of the balloon 44. The guidewire lumen 48 is influid communication with a guidewire distal port 49 at the distal end ofthe shaft 41, and with a guidewire proximal port (not shown) at aproximal end of the shaft 41. An adapter 50 at the proximal end ofcatheter shaft 41 is configured to provide access to guidewire lumen 48,and to direct inflation fluid into inflation lumen 46 through arm 51. Inaccordance with the invention, inner tubular member 47 has a stiffnesstransition and a bonded portion 60, as discussed above in relation tothe embodiment of FIG. 1. In the embodiment of FIG. 6, the bondedportion 60 having a length of about 0.1 to about 2 cm, is about 0.07% toabout 1.5% of the length of the inner tubular member (the inner tubularmember having a length of about 135 to about 145 cm).

Although illustrated as one-piece tubular members, it should beunderstood that the tubular members forming the catheter shaft 11, 41may be formed of multiple tubular members or multilayered tubularmembers. For example, the outer tubular member 19, 45 may comprisemultiple tubular members joined end to end, providing increasingflexibility distally along the length of the catheter.

To the extent not previously discussed herein, the various cathetercomponents may be formed and joined by conventional materials andmethods. For example, the tubular members forming the catheter shaft 11,41 can be formed by conventional techniques, such as by extruding andnecking materials found useful in intravascular catheters such aspolyethylene, polyvinyl chloride, polyesters, polyamide, polyimides,polyurethanes, polyether block amides, and composite materials.

The length of the balloon catheter 10, 40 is generally about 137 toabout 145 centimeters, and typically about 143 centimeters for PTCA. Theouter tubular member 19, 45 proximal section has an OD of about 0.036 toabout 0.043 inch (0.91-1.1 mm), and an inner diameter (ID) of about0.032 to about 0.036 inch (0.81-0.91 mm), and the outer tubular member19, 45 distal section has an outer diameter (OD) of about 0.028 to about0.036 inch (0.70-0.91 mm), and an inner diameter (ID) of about 0.024 toabout 0.035 inch (0.60-0.89 mm). The inner tubular member 20, 47 has anOD of about 0.017 to about 0.026 inch (0.43-0.66 mm), and an ID of about0.015 to about 0.019 inch (0.38-0.48 mm) depending on the diameter ofthe guidewire to be used with the catheter. The balloon 14, 44 has alength of about 8 mm to about 40 mm, and an inflated working diameter ofabout 1.5 mm to about 5 mm.

While the present invention has been described herein in terms ofcertain preferred embodiments, those skilled in the art will recognizethat modifications and improvements may be made without departing fromthe scope of the invention. Moreover, while individual features of oneembodiment of the invention may be discussed or shown in the drawings ofthe one embodiment and not in other embodiments, it should be apparentthat individual features of one embodiment may be combined with one ormore features of another embodiment or features from a plurality ofembodiments.

1-31. (canceled)
 32. A balloon catheter having an elongated shaft with a proximal end and a distal end and a balloon on a distal shaft section, the elongated shaft comprising: an outer tubular member defining at least a section of an inflation lumen in fluid communication with an interior of the balloon, and having a proximal end and a distal end; and an inner tubular member defining at least a section of a guidewire lumen, extending in at least a distal section of the outer tubular member and extending in the interior of the balloon, the inner tubular member having a proximal end, a distal end distal to the distal end of the outer tubular member, a length, a bonded portion along which an outer surface of the inner tubular member is bonded to an inner surface of the outer tubular member, a proximal portion proximal to the bonded portion, and distal portion distal to the bonded portion, the proximal portion of the inner tubular member having an axial compression stiffness less than an axial compression stiffness of the distal portion of the inner tubular member.
 33. The balloon catheter of claim 32 wherein the bonded portion has a distal end located proximal to the balloon.
 34. The balloon catheter of claim 32 wherein the bonded portion has a proximal end located distal to a guidewire proximal port in fluid communication with the guidewire lumen.
 35. The balloon catheter of claim 32 wherein the bonded portion has a length of about 0.1 to about 2 mm.
 36. The balloon catheter of claim 32 wherein the inner tubular member proximal end is located distal to the proximal end of the shaft in the distal shaft section, and the bonded portion has a length which is about 0.4% to about 8% of the length of the inner tubular member.
 37. The balloon catheter of claim 32 wherein the inner tubular member proximal end is located at a proximal end portion of the shaft so that the inner tubular member extends along a proximal shaft section and the distal shaft section, and the bonded portion has a length which is about 0.07% to about 1.5% of the length of the inner tubular member.
 38. The balloon catheter of claim 32 wherein the proximal portion of the inner tubular member has a bending stiffness less than a bending stiffness of the distal portion of the inner tubular member.
 39. The balloon catheter of claim 32 wherein at least part of the inner tubular member proximal portion has a first wall thickness, and at least part of the inner tubular member distal portion has a second wall thickness which is greater than the first wall thickness.
 40. The balloon catheter of claim 39 wherein the part of the inner tubular member having the first wall thickness has an outer diameter smaller than an outer diameter of the part of the inner tubular member having the second wall thickness.
 41. The balloon catheter of claim 39 wherein a wall thickness of the inner tubular member along the bonded portion is greater than the wall thickness of the inner tubular member proximal portion.
 42. The balloon catheter of claim 32 wherein at least part of the inner tubular member distal portion is formed of a polymeric tube having at least one layer with fiber reinforcement therein.
 43. The balloon catheter of claim 32 wherein the inner tubular member proximal portion comprises a first polymeric material having a first Shore durometer hardness, and the inner tubular member distal portion comprises a second polymeric material having a second Shore durometer hardness which is greater than the first Shore durometer hardness.
 44. The balloon catheter of claim 32 wherein the inner tubular member comprises a polymeric tube with a coiled reinforcing member embedded in at least a section thereof.
 45. The balloon catheter of claim 44 wherein the coiled reinforcing member extends along an entire length of the inner tubular member.
 46. The balloon catheter of claim 44 wherein the coiled reinforcing member extends at least in part within the proximal and distal portions of the inner tubular member.
 47. The balloon catheter of claim 32 wherein the bonded portion extends around part of a circumference of the inner tubular member, so that a nonbonded portion of the inner tubular member is radially adjacent to the bonded portion.
 48. The balloon catheter of claim 47 wherein the bonded portion extends around about 10% to about 90% of the circumference of the inner tubular member.
 49. The balloon catheter of claim 32 wherein the inner tubular member comprises a polymeric tube with a reinforcing member bonded thereto.
 50. The balloon catheter of claim 49 wherein the reinforcing member is coiled. 